Apparatus for determining the speed of flight of aircraft



April`18, 1933.

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.APPARATUS FOR DETERMINING THE SPEED 0F FLIGHT 0F AIRCRAFT Filed July 8, 1930 Patented Apr. 18, 1933 UNITED 'STATES PATENT oFFicE CHRISTIAN von HOFE, OI AVIENNA, AUSTRIA, AND JOHANN BOYKOW, OF BERLIN- LICHTERFELDE, GERMANY, ASBIGNOBS TO CZEGHOSLOVAK COMPANY: AOIIEN- GESELLSCHAFT C. P. GOEBZ OPTISCHE ANSTALT .AGTIOVA SPOLECNOST K. '.P. GOEBZ OPTIOKY USTAV, F PRESSB'UBG, CZECHOSLOVAKIA arrnna'rus ron nn'rnnmme 'rim SPEED or ruenr or Ircam Application led July 8, 1080, Serial No. 488,496,1and 1n Germany July 13, 1929.

The shellldropping apparatus constructed in accordance with the U. S. Patent No. 1,7 03,386 is not only adapted for determining the line of sight intersecting the tar et 5 at that moment at which the shell has to dropped for hitting the target, but also for determining the speed of Hight of the aircraft above the ground, provided however, that there is in the direction of the 1i.ight,in

front of the observer a readily observable stationary object or point of reference. Otherwise, for instance in case of `a flight above the ocean, such a stationary object can be provided only by dro ping a iioating' structure visible at great istances, but the floating structure serving as a point of reference will then naturally appear in rear instead of in front of the observer so that with such a dropping device it is impossible to determine the s ed of the air craft.

The object o the resent invention is to adapt the apparatus a ove referred to for determining the speed of the aircraft even if the point of reference is in rear of the observer. This ob'ect is arrived at according to the invention y turning the dropping device around a vertical axis throu h an angle of at least 180 and simultaneous reversing the direction of movement for operatlng the 3o entering reflector by means of -a reversing gearin provided in the clockwork actuating the re ector so that the point of reference lagging behind the reflector comes into eoincidence in the field of vision of the observation telescope which is rovided with a water level, with the air ubble ofthe water level for the first time at the beginning an for the second time at the end of a measuring period, thus permitting to determine 4o from the duration of-the measuring peri and from the given height of the aircraft above the ground the. speed of flight 'of the aircraft.

A constructional form of the invention is illustrated by way ofexamplein the annexed drawin Fig. l'represents the theoretical basis o the invention, Fig. 2 is a side elevation partly in section and Fig. 3 is a plan view partly in section of a preferred form of our invention. i

It is assumed with reference to Fig. 1 that the 'aircraft is stationary at the point F in the height BF=k above the ground, while ,the ground or the surface of the sea with the target moves backwards, that is to say to the right of the aircraft. The angle between the sight line to the target andthe vertical is p1 at the beginni and pz at the end of the measuring periodn during which the target moves from Z1 to Z2 if 1t is in front of the observer. If, however, the target consists of a oating structure dropped from the aircraft and therefore is in rear of the observer, it will be at lZ1 at the beginning ald at Z2 at the end of the measuring period, the corresponding angles being pl and pz respectively. For determ' the angles of inclination of the line of sig t at any time existilg we arrange at a redeteb' mined distance ofthe sight line a rectilinear guide PDQ, for a pivot pointP1 by which the si ht line is guided. If from the beginning o .the measuring 'period a uniform movement is imparted by a clockwork to the point P1 of intersection of the sight line with Z1B of tlietar et along the path moves at first more quic y and t en more slowly than the target so that after a certain time T the the path target being in the point z, fans again in the u 7 opositively turned sight line FZz, at which ik moment the angle of inclination of the sight line and the vertical will be 'qu'. The way through which the target has moved during this measuring period is defined by Z1Z=v (tan (P1-tan 3). l Exactly the-same result is obtained the target in rear of the observer which is at Z1 at I and at Z," at theendoftheao vms l 110 from the pivo' point F lo the point I5 l wherein the measuring time and c is the uniform speed of the movement of the point P1 or P1. Hence From the above it will be understood that the triangle FZ1" Z2 for a target in rear of the observer is obtained by turning the triangle F Z1 Z2 for a target in front of the observer around a vertical F B through an angle of 180- reversing at the same time the movement of the point P1 asa point of the sight line FZI at the beginning of the measuring period as compared with the direction bf movement of the point P1.

Now it will be understood that for adjusting the sight line angles p1 p2 and p1 pz direction of movement PDQ, POQ sight line points P1 P2 and P1 P2 may be selected at will asvlong as by any suitalle means, for instance gear wheels, the angles FP,L P0, FPz Po and FP1 P0', FP2 P0 are correctly transmitted to theyoptical line of sight as is effected in the constructional form of our apparatusshown in Figs. 2 and 3. In Figs. 2 and 3, 1 is the objective and 2 the eye piece of the telescope in the casing of which a rotatable entering reHector 3 is mounted in lfront of a .window 4 on horizontal trunnions 5. Secured to the reHector frame is a toothed segment 6 which meshes with a toothed segment 7 of half the radius of the .segment 6. The segment 7 is pivoted on journal pin F and rigidly connected to a link 8 provided with a longitudinal rectilinear slot into which engages'the pin P of a nut 9 engaging a screw spindle 10 but xlocked against rotation. The screw spindle ment of which is transmitted to the crank 15 by means of a shaft 14 whereby the medium of the push bar 16 the direction of rotation of the clock work shaft 17 is reversed in any well known manner not illustrated. On the shaft 17 is mounted a spur wheel 18 engagin into a spur wheel 19 fast on the screw spmdle 10. The uniform rotary movement of the shaft 17 is transmitted in any known or preferred manner to a pointer 20 moving along the scale 12a in the one or in the other direction according to the position of the reversing lever 13. The clockwork 12 may be wound up by a handle 21 while the handle 10a secured to the screw spindle 10 serves for adjusting the pointers 8a and 20. For securing a vertical position` of the telescope a transparent focus water level 22 serving as a collective lens is provided in the image plane of the telescope so thatV the air bubble of the water level appears on the targets image rectified by the prism 23.

In order to enable the instrument above described to rotate around a vertical axis M, its casing is provided at its lower part with a tubular extension H freely rotatable by hand in a stationary bearing S.

For determining the speed of Hight the apparatus is used as follows:

When ahead of the aircraft Hying at a given height appears a clearly visible target the reversing lever 13 is brought to its forward position (fu) and by rotating the handle 10a the pointer 8a is adjusted on the scale 11a in accordance with the height of Hight whereby to the line of sight the angle of inclination p1 is imparted. Now the aircraft Hies towards the target so that the ima e of the target continuously a proaches tigre air bubble of the water level. t the moment when the two come in coincidence, the clockwork is started by pressing the button 24 in the usual manner whereupon the image of the target first recedes from the air bubble of the water level, but then again approaches thesame. At the moment when the image of the target again coincides with the air bubble of the waterflevel the clockwork is stopped by depressing the button 24 and hence the pointer 8b on the scale 11b indicates a value corresponding to the angle p.

Now from Fig. 1 We find that Therefore the speed of Hight to be determined is tan 02:

The period of time T, however, is the same as that `which the clockwork would require for moving the point or journal pin P with Lacasse t being the time required for moving through the distance P1 P2 or Z1 Z2, that is to say the period of time between the two coincidences of the image of the target with the air bubble of the water level.

Makingl= 100 metres per second and -hence for instance for h=3000 metres the time T=30 seconds, then from the abov equation the speed of flight is v-J tan go2= 100 tan gaz.

Hence if besidesA thel scale 11a for the heights the scale 11" for tan p1 is provided on the back of'11 the end of the lmk 8 being constructed as a bifurcated double pointer 8a., 8b, then, if thel period of time T is properly selected, say f T 100 and the scale 11b is correspondingly proportioned as 100 times the value of tan p1, the reading on this scale gives directly the value of the speed of flight. For adjusting the inclinationp1,it is of course not necessary to .zause the clockwork to run until the point P has moved from P0 to P1. It is suicient to move the point P1 by turning the handle 10a.

In a similar manner the speed of flight can be determined in the case o flight above the ocean inwhich case by dropping a floating structure, a visible point of reference is established in rear ofthe aircraft. It has to be borne in mind that for proper adjusting the apparatus has to be turned around a ver' tical axis through an angle of 180 and the reversing lever 13 has to be brought to the backward position (R) whereby the movement .of the clockwork or the pointers 8a and 20 is reversed. When the auxiliary target is located in the rear of the aircraft, the sight line going to the target must first be adjusted to the angle qu in order that, as before in the 'case of an auxiliary target located ahead of the aircraft, at the moment when the ima e of the target'comes into coincidence 'with t e air bubble of the vwater level, the clockwork may be started by depressing the button 24. Owing to the movement ofthe entering reilector 3 then beginning, the image of the tart will first leave the air bubble of the water evel and then again approach this air bubble and at the moment when the tar t im- 'age again coincides with the air bub le the the starting value BZl by turning clockwork is stopped by again depressing the button 24. At this latter moment the line of sight to the target is inclined at the angle rpz'.

The adjustment for the first angle is effected in this case by the transparent pointer 20 which is provided with a reading mark on the scale disc 12a provided with two circular scales. One of these scales, for instance the outer one, has a division for tan p1, preferably numbered by the reciprocal cot p values, which serves for adjusting the pointer 20 to the handle 10a.

hence v :h am al' h T cot gol T By taking preferably BZ1 CO th (p1, 1000 metres and for a height of light h of for instance 3000 metres, the valueY of A and can be read by means of the pointer mark on the inner scale 12a numbered by v thousand times the reciprocal values of the timev T.

What We claim is:

1. Apparatus for determining the speed of flight of air-crafts for use with auxiliary targets ahead of, or in the rear of the said -aircrafts comprising a sighting telescope.; an entering reflector for the said sighting telescope comprising a rotatablepointer, means for rotating the said pointer and for simultaneously rotating the said entering reflector of the telescope, the last named means comrising a clock work, a spindle and a gear- 111g for driving the said spindle by the said clock work, and means for starting, stopping and reversing the direction of movement of of the telescope, the last-named means comprising a clock work, a spindle and a gearin l for driving the said spindle by the said cloc work, and means for starting, stopping and reversing the direction of movement of the said spindle; a reading scale for the said pointer for use with auxiliary targets ahead of the said aircraft; a reading scale for the said pointer for use with auxiliary targets in rear of the said aircrafts and means for turning the apparatus as an entirety around a vertical axis through an angle of at least 180.

3. Apparatus for determining the eed of flight of aircrafts for use with a iary targets ahead of or in the rear of the said aircrafts, comprising a sighting telescope; an entering reiector for the said sighting telescope comprising a rotatable pointer, means for rotating the said pointer and for simultaneously rotating the said enterin reiiector of the telescope, the last-name means comprising 'a clock work, a spindle and a gearing for driving the said spindle by the said clock Work, and means for starting, stopping and reversing the direction of movemeant of the said spindle; a reading scale for the said pointer for use with auxiliary targets ahead of the said aircrafts; a reading scale for the said pointer for use with auxiliary targets in rear of the said aircrafts, thesaid readingscales being arrangedonrone dial; and means for turning the apparatus as' an entirety around a vertical axis through an angle of at least 1 In testimony whereof We have axed our signatures. Y

CHRISTIAN VONHOFE. JOHANN BOYKGW. 

